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chemicals released with the cooling water (Clark and Brownell, 1973; 

 Marcy, 1975; EPA, 1977a). New Haven Harbor Station does not utilize 

 biocides in its cooling Water system. 



Of the two potential sources of impact, power plant passage 

 has been considered to pose the more serious problem (Miller and Beck, 

 1975) . Zooplankton (including ichthyoplankton) mortalities due to plant 

 passage range from to 100% (Marcy, 1975; Jeffries and Johnson, 1976; 

 Cannon et al . , 1978). Recent studies have indicated that entrainment 

 mortalities were low at temperatures below theirmal tolerance limits for 

 species tested and increased as lethal thermal thresholds (generally 

 30°C) were approached and exceeded (Cannon et al . , 1978). Though it 

 probably reflects a substantial overestimate of the loss due to entrain- 

 ment (cropping) , assumption of 100% entrainment mortality certainly pre- 

 sents the worst-possible situation regarding entrainment effects. If 

 entrainment loss projections based on 100% mortality are within an 

 acceptable level, then further effort to define precise mortality in a 

 given system is unnecessary. Furthermore, survivors of plant-passage 

 stresses may be more susceptible to infection, predation, and develop- 

 mental aberrations than organisms not subjected to passage through the 

 cooling system (Clark and Brownell, 1973; Ulanowicz, 1975) . 



It is difficult to directly address the question of how well 

 natural populations can accomodate attrition rates associated with 

 power-plant passage. Enright (1977) , for example, has pointed out that 

 obtaining estimates of the quantities of meroplankters passing through a 

 power-plant cooling system has little practical value since the rela- 

 tionship between such quantities (assumed to represent total losses) and 

 post-larval recruitment is rather obscure. To evaluate power-plant 

 impact on attached or infaunal organisms, Enright (1977) recommends 

 investigation of changes in rates of post-larval settlement on arti- 

 ficially prepared substrates. This general approach was utilized in the 

 exposure panel studies presented in Section 5 of this report. Further 

 guidance with regard to this question has been provided by the US EPA 

 (1977b). Specifically, EPA (1977b) states: 



